Merge topic 'cmake-upload-junit-reports' into release-3.21

cb5c03ed04 gitlab-ci: upload JUnit reports for builds
722270ff50 ci: update to 3.21.0-rc2 for CI usage

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: Craig Scott <craig.scott@crascit.com>
Merge-request: !6072